Great frigatebird description

With the largest wing area to body mass ratio of any bird, frigatebirds are wonderfully adapted for an aerial lifestyle (3). These birds have a distinctive scissor-shaped tail and greatly elongated angular wings, allowing them to make spectacular flight manoeuvres and soar almost effortlessly above the ocean (3)(4). Frigatebirds are also the only seabird family that display obvious, significant differences in plumage between the sexes (4). The male great frigatebird is all black with a glossy green and purple sheen on the head, neck and upper back, apart from a faint pale brown bar on the wings and, like other male frigatebirds, possesses a large, red gular pouch that is blown up like a balloon during displays to attract a mate. The female is larger than the male, has a less glossy sheen to the black feathers, has a gular pouch that is not distensible, and has a white upper breast and a light grey throat, and a pale brown bar on the wings. The juvenile has a reddish-brown patch on the head and white undersides, and displays a number of immature plumages before eventually taking on that of the adult (2). While perfectly adapted for magnificent flight manoeuvres, the great frigatebird is less impressive on land and sea (4). It has short legs and very small feet, making movements on land quite awkward, while the plumage lacks a waterproof coating and the feet are un-webbed, meaning this bird spends no time on the water. If it sits on the water for more than a minute or two it has great difficulty getting into the air owing to wet plumage (3)(4).

Related species

Great frigatebird biology

Frigatebirds are remarkable for being capable of staying in flight for extended periods, covering several days and nights, and may even sleep while on the wing. Like other frigatebirds, this species uses thermals to soar to heights of up to 2,500 metres, gliding downwards and climbing again in succession, with little need for wing flapping. This effortless flight allows long distances to be covered with minimal energetic cost (3).

The lack of waterproof plumage means that this species obtains most of its prey either just above, floating on, or submerged a few centimetres below the water surface. As such, its main source of prey is flying fish (airborne or just beneath the surface), but it also takes squid, jellyfish and scraps discarded by boats, and will often feed over tuna and other predatory fish that drive smaller fish species to the surface (2)(4). In addition to catching prey, the greater frigatebird will sometimes harass other bird species on the wing, forcing them to release food that they have recently caught, which is then snatched from mid-air before it reaches the water (2)(4). When not airborne, the great frigatebird perches in trees, bushes or, less preferably, on the ground. A gregarious species, roosting takes place in large colonies, where, during the day, individuals may display a remarkable sunning posture, involving sitting upright with the wing undersides rotated upwards while fully extended to the sides, exposing the chest and underwings to the sun (4).

The breeding behaviour of the great frigatebird is highly unusual and dramatic. During courtship, the males gather in groups of various sizes, with gular pouches inflated, bills clattering, and wings and heads waving, while calling to attract females flying overhead. Once a pair decides to mate, they snake necks together and nibble at each others feathers, before commencing the construction of a nest. The male provides material such as twigs, while the female does the actual building, but both birds defend the nest from intruders or theft of nesting material by other males (4). After mating, a single white egg is laid, which is incubated in turns for 51 to 57 days by both the male and female (5). The chick, which takes around 17 to 24 weeks to fledge, may be fed by both parents for an additional 5 to 18 months (2). This extended period of parental care exhibited by all frigatebirds is the longest of all birds, and means that a pair can only breed in alternate years. However, despite this intense level of parent care, many chicks starve to death within months of becoming fully independent because they do not learn to feed themselves. Some areas in which they nest are severely affected by the occurrence of El Niño events, during which many young starve to death as the local fish move elsewhere and good fishing skills become even more important (4).

Great frigatebird range

The great frigatebird is a widespread seabird, with breeding colonies found on isolated islands in the tropical and sub-tropical waters of the Pacific and Indian Oceans. It also used to breed on the Brazilian islands of Trindade and Martin Vaz in the Southern Atlantic, but there are no recent records of this (5)(6).

Great frigatebird status

Great frigatebird threats

With an extremely large range and population, estimated at half a million to one million birds, the great frigatebird is not currently considered to be at risk of extinction (2)(6). However, some populations are thought to be decreasing, most likely due to a combination of habitat destruction, from the loss of nesting trees to cultivation or tourist developments, and disturbance. In some areas, predation of eggs and chicks by introduced predators and direct persecution by humans for food is also a threat (2)(5). This decline has been most notable within the Atlantic subspecies, Fregata minor minor, which is now absent on St Helena, with no recent breeding records from the other islands which it occupies, suggesting that this subspecies may be on the verge of extinction. The Christmas Island population could also become extinct within the next 20 years due to overharvesting for food, while the colony on Aldabra Island was extirpated by impacts from tourists, but was later recolonised after conservation efforts (5). The great frigatebird is also threatened by the occasional severe storms that are caused by the El Niño, which can cause partial or total breeding failure and starvation in juveniles (2)(5). These threats are compounded by the species’ very slow reproductive rate, and a large drop in a population may go unnoticed for several years due to its long lifespan (2).

Great frigatebird conservation

The great frigatebird is found in a number of protected areas throughout its range, including on several Hawaiian Islands, the Republic of Kiribati and the Cocos Islands. It is also protected by law in many areas where it occurs, although law enforcement can prove challenging on remote, isolated islands and the level of protection afforded this species varies greatly. Conservation priorities for the great frigatebird are further surveys to determine population numbers and status, so that informed conservation recommendations can me made and enforced protection of conservation laws (5).

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Glossary

El Niño

A natural phenomenon that happens every 4 to 12 years, and lasts for several months, when upwelling of cold, nutrient-rich water does not occur. This causes the warming of ocean surface water off the western coast of South America and causes die-offs of plankton and fish. It also affects Pacific jet stream winds, altering storm tracks and creating unusual weather patterns in various parts of the world.

Gular pouch

A large distensible pouch below the beak of some birds.

Incubate

To keep eggs warm so that development is possible.

Subspecies

A population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.

Thermals

Masses of heated air which rise to several thousand feet, and may be used by birds, insects and man to gain altitude and exploit higher altitude winds.

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